1. Field of the Invention
The present invention relates to a method of manufacturing a non-resonance knock sensor and an apparatus of manufacturing the same.
2. Description of Related Art
JP-A-2000-249598 discloses a non-resonance knock sensor. The non-resonance knock sensor is composed of various components, as shown in FIGS. 12, 13 and 14. FIG. 12 is a sectional view of a assembly body of a non-resonance knock sensor before resin mold process. FIG. 13 is a sectional view of a sensor main body of the non-resonance knock sensor after the resin mold process. FIG. 14 is an exploded perspective view of the assembly body of FIG. 12.
As shown in FIGS. 12 to 14, a cylindrical base 1 made of metal such as iron is integrally provided at a lower end thereof with a flange 1a. The cylindrical base 1 is provided around an outer circumference at an upper end thereof and around an outer circumference of the flange 1a with a piece or plurality pieces of annular grooves 1b, respectively, for assuring sealing characteristic with mold resin. The cylindrical base is further provided around an outer circumference thereof below the annular grooves 1b on an upper end side with a male thread to which a nut 2 is fastened.
A ring shaped insulator 3A, a ring shaped terminal plate 4A, a ring shaped piezoelectric element 5, a ring shaped terminal plate 4B and a ring shaped insulator 3B are inserted to the cylindrical base 1 in order so as to be piled on top of one another. Electrodes of the piezoelectric element 5 at upper and lower faces thereof are in contact respectively with the terminal plates 4A and 4B. The terminal plates 4A and 4B are provided respectively with terminals 5a extending in the same direction. A resistor is connected between the terminals 4a. 
As shown in FIGS. 12 to 14, the nut 2 is composed of an upper end cylindrical portion whose inner circumference has a female thread, a lower end ring shaped weight 2b and a thin thickness cylindrical portion 2a bridging between the upper end cylindrical portion and the ring shaped weight 2b. The thin thickness cylindrical portion 2a is formed in shape of a taper whose diameter is larger toward the ring shaped weight 2b. An inner diameter of the ring shaped weight 2b is larger than an outer diameter of the upper end cylindrical portion. Wall thickness of the thin thickness cylindrical portion 2a is below 2 mm or thinner than that of the ring shaped weight 2b for securing its resiliency. The insulators 3A and 3B, the terminal plates 4A and 4B and the piezoelectric element 5 are sandwiched and pressed between the ring shaped weight 2b and the flange 1a and covered with mold resin 7.
Inner and outer diameters of the ring shaped weight 2b are substantially same to those of the insulators 3A and 3B, the terminal plates 4A and 4B and the piezoelectric element 5. A preset load is applied axially from an entire lower end surface of the ring shaped weight 2b to an entire surface of the piezoelectric element 5. The ring shaped weight 2b is provided at a plurality of portions, typically at two portions, on an upper side outer circumference thereof with cuts 2c, to which a fastening tool is fitted for fastening the nut 2.
As shown in FIG. 15 as a general idea, an automatic assembly line for manufacturing the non-resonance knock sensor mentioned above has an assembling stage 10 where the insulator 3A, the terminal plate 4A, the piezoelectric element 5, the terminal plate 4B, the insulator 3B are inserted piece by piece sequentially to the cylindrical base 1, a fastening stage 11 where the components piled up on top of one another at the assembling stage are fastened with the nut 2 and fixed to one another, a bending stage 12 where the terminals 4a of the terminal plates 4A and 4B are bent, and a welding stage 13 where the resistor 6 is connected by welding between the terminals 4a. The assembling stage 10, the fastening stage 11, the bending stage 12 and the welding stage 13 are arranged in straight. The automatic assembly line further has a resin molding stage 14 adjacent to the welding stage 13, an anneal furnace 15 positioned on the back of the resin molding stage 14 and a series of a leak check stage 16, an insulation check stage and a performance check stage.
A horizontal floor area necessary for installing the automatic assembly line mentioned above is about 98 m2 as a calculation, in spite of a relatively small body of the non-resonance knock sensor whose size is about 3 cm×6 cm.